Since the listing of the Model S, it seems to have been dismantled numerous times, which also confirms Tesla's position as the benchmark in the early days of the electric vehicle market.
First, the powertrain constitutes:Model S powertrain is mainly divided into these parts: power battery system ESS, AC induction motor Drive Unit, vehicle charger Charger, high voltage distribution box HV JuncTIon Box, heater PTC heater, air conditioning compressor A/C compressor and DC Converter DCDC.
The Model S uses a three-phase AC induction motor and integrates the motor controller, motor, and gearbox. In particular, the motor controller is also packaged in a cylindrical shape that corresponds to the motor and looks like a dual motor. From the design point of view, the integration is high and the symmetry is beautiful. The intermediate gearbox uses a fixed ratio (9.73:1) solution. The 85KWh version has a peak motor power of 270 kW and a torque of 440 Nm.
The charging system supports three charging methods:
1. Super charging pile DC fast charge
The super charging pile can directly output 120KW to charge the ESS and can be filled within one hour.
2. High power wall charging
There are two car chargers under the rear seats, one master and one slave. The main charger is the default open use, power 10KW, almost full 8 hours. Although the hardware of the slave charger has been installed in the car, it needs to pay an additional 18,000 to activate, which can double the charging capacity. This kind of hardware has already been configured, and then the license fee is the same as IBM's server. At present, Tesla has used this strategy on the power battery. The 60 version has actually installed more than 70 kWh of electricity. The reserved capacity is just enough to avoid full charge, which helps to extend battery life, so the low-end version is also a There are cost-effective options.
3.220V household socket charging
The charging power is about 3kw, and it is fully charged for about 30 hours. Put the charger in the car, even if you don't have a charging infrastructure, you can use the ordinary household plug to charge.
The interesting part of the thermal management part is that the Model S uses a four-way switching valve to achieve series-parallel switching of the cooling system. The purpose of my analysis is mainly to select the optimal thermal management method according to the working conditions. When the battery needs to be heated at a low temperature, the motor cooling circuit is connected in series with the battery cooling circuit, so that the motor heats the battery. When the power battery is at a high temperature, the motor cooling circuit is connected in parallel with the battery cooling circuit, and the two cooling systems independently dissipate heat. This kind of thermal management is still quite clever.
First look at the battery pack (PACK) before the disassembly, there are a total of three sets of interfaces. They are low-voltage interface, high-voltage interface, cooling interface, and all adopt the quick-release solution. It shows that Tesla fully considered the technical requirements of the power-changing mode when designing the battery system. Even if there is very little need to change the power, this gene has always been retained. The thicker Pin in the high voltage connector plays a role in positioning and is also a grounding point. The thin Pin is used to realize the high voltage interlock function.
The top surface of the PACK is designed with a waterproof and breathable valve. The difference between the size of the gas molecules and the liquid and dust particles allows the gas molecules to pass through, and the liquid and dust cannot pass, thus achieving the purpose of waterproofing and venting, avoiding water vapor in the PACK. Internal condensation.
A large number of fixing screws are used in the upper part of the PACK, so the white insulating pad is glued to the PACK, and in addition to the function of insulation and fire prevention, it can also play a certain waterproof function. The top cover of the PACK is glued to death, and it cannot be opened even if all the screws are removed. I remember that in the hot summer of 14 years, our seven or eight people were "stubborn" for an hour before they could be destructively opened. At that time, I felt that Tesla must be considered in the design of the car, and did not intend to repair afterwards, so there is no manual maintenance switch on the PACK, leaving only a fuse replacement port.
The Tesla lower tray uses aluminum alloy profiles as the main frame-type skeleton, and the bottom of the skeleton is welded with a single piece of aluminum. Disassembled is a high-profile version of 85KWH, with two modules (Module) stacked on the far right. A large number of explosion-proof valves (85 in total) are arranged on both sides of the PACK. In the process of dismantling, it is found that the PACK always uses a loose insulating plate to separate the high-voltage devices. The way to fix the insulating plate is usually glue. It is like using a dog skin plaster to fill the PACK inside. It is hard to imagine that it is so complicated. How the process works during the mass production process. Guessing is that the lack of consideration at the beginning of the design led to the subsequent helpless way to patch.
The Battery Management System (BMS) is almost completely exposed inside the PACK, perhaps to reduce weight, but it also poses certain risks.
The water cooling system between the modules uses a parallel structure instead of being connected in series, the purpose of which is to ensure that the coolant flowing into each Module has a similar temperature.
The high-voltage electrical connections between the modules are arranged in a left-right staggered arrangement, rather than a relatively simple connection from the PACK tail to the top and back to the tail. The guess is to prevent the formation of large current loops resulting in strong radiated interference.
Current sampling uses only one ISAscale industrial grade Shunt to communicate with the BMU over the SPI bus. Previously, the solution for the A123 power battery on the Roewe E50 was based on the dual backup of shunt and Hall. After all, the current value is an extremely critical parameter in the ESS system.
Third, the battery Module
Thanks to the use of NCA's batteries, Tesla is far ahead in energy density, and the energy density of Pack is higher than that of many models. The figure below shows the difference between the high and low modules. The low module has 10 cells each, and the number of series is 6 strings, so there is not much difference in battery management. It can be seen from the manifold that the color of the part connected to the Busbar is significantly different. Here, the surface is nickel-plated to prevent oxidation.
Due to the selection of the 18650 battery by Tesla, the design of the module heat exchanger must inevitably result in the design of the Coolant pipe being extremely complicated, and the battery is firmly fixed in the Module with glue, and there is no possibility of maintenance and ladder utilization. The use of square batteries I3 and Volt makes it easier to integrate the cell and cooling system.
The Volt has designed a heat dissipation layer between each cell, which makes the heat exchange area larger and better. It is speculated that this solution may become the mainstream in the future.
Fourth, battery management system BMSThe BMS adopts a master-slave architecture, and the main controller (BMU) is responsible for high voltage, insulation detection, high voltage interlock, contactor control, and external communication. The slave controller (BMB) is responsible for the single-cell voltage and temperature detection and reports to the BMU.
The BMU has a primary and secondary dual MCU design, and the secondary MCU can detect the working status of the primary MCU, and can obtain control authority once it is found to be invalid. The more humorous thing is that there is a manual reset button on the BMU. When I saw it, I couldn't believe it was a car-level ECU, more like a computer motherboard. It is also a bold design to place the pre-charged contactor with excessive current current directly on the BMU.
The following picture shows the comparison of the module monitoring BMB of Tesla, BMW i3 and A123. The specific parameters are as follows:
Legend has it that Tesla has detected more than 7,000 knots of battery voltage. In fact, only 74 cells are connected in parallel for detection. It is said that the temperature of each cell is monitored. In fact, there are only two temperature detection points for the 444 cells. Legend has it that every battery can be balanced, in fact, the current is only 0.1A, for a 230Ah battery. Especially in the voltage monitoring redundancy design, BMW (preh) uses LT6801, A123 uses IC8 for hardware comparison, once the MCU fails or communication is abnormal, it can trigger alarm directly on the hardware. In contrast, Tesla is designed to be simpler. In particular, the use of UART communication instead of CAN is more like a solution for IT companies.
Five, single battery Cell
From the Spec provided by Panasonic, the 68% reduction in capacity after 500 cycles after 0.5 cycles at 0.5C charge / 1C discharge (100% DOD), the attenuation is more serious.
The same is the 1C/1C charge and discharge 150cycle experiment, the comparison of the I3 and Model S batteries above. The above several cycle life data is a good example of why the Model S is groundbreaking in the passenger car with a huge battery of 85kwh. Because the Panasonic 18650 battery has a poor cycle life at a rate of around 1C. Therefore, it is necessary to pass the high capacity to reduce the magnification under the same working conditions, and to ensure a longer cycle life; at the same time, the large-capacity battery also ensures that the number of cycles of the vehicle is sufficiently small throughout the life cycle. Calculated according to the electric power consumption of 20KWH per 100 kilometers, 200,000 kilometers is only 470cycles for the PACK of 85KWH.
As more battery companies standardize and mass-produce custom batteries for the automotive industry, the advantages of low cost and high consistency of the 18650 battery will quickly disappear, even though Tesla once hoped to open the technical route team through open patents. It seems to be unsuccessful. The opening of patent gimmicks and publicity effects is greater than the actual significance.
However, in the era when the electric vehicle supply chain was still immature, Tesla relied on excellent technical integration ideas to “make up†an inter-generational product in various non-automotive selections. Therefore, it is hard to say that Tesla is better than traditional car companies in power batteries. It is better to say that Tesla did what they dare not do; the traditional supply chain system of the traditional car enterprises, the long-term accumulation of standard specifications, and the huge market share. These aspects have become a burden on the promotion of electric vehicles. Tesla can give up the auto supply chain without any burden. It can temporarily select Autosar, ISO26262, etc., instead of worrying about the electric car technology going too aggressively, causing fires like traditional car companies. Accidents such as out of control affect the sales of traditional models. But since then, the competitive advantage of Tesla and traditional car companies is still a solution under the constraints of this historical condition? I think definitely not.
Once you look at the product from the standpoint of the engineer, you can often reveal the perfection that the company wants to create. After all, the process of product design is necessarily a process of compromise and trade-off, and enterprises often try to use concepts such as “not compromiseâ€, “not to be†(such as some mobile phone companies in China), and design The essence is contrary. But when you are a consumer, Tesla still has a strong appeal to me. The source of attraction is not the use of advanced or backward technology; it is above the technical stack and performance parameters. Product temperament, this temperament is the feeling that many people want and other models can not give, I think this is the most successful place of Tesla.
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